The research objectives of this project are to analyze interactions among the neural tube, its vascularization, and the surrounding chordamesoderm during normal and abnormal development. The fine structure and cellular kinetics of the normal and abnormal neural tube prior to and during closure will be investigated by means of scanning and transmission electron microscopy and autoradiography. The effects of early proliferative disorders on subsequent differentiation of neural tissue and on the maturation of cerebrovascular elements will also be studied, and interactions between the neural tube and chordamesodermal tissue will be analyzed in terms of the extracellular matrix, including glycosaminoglycan deposition in basal laminae. The project will involve abnormalities induced experimentally in the chick, as well as those which occur in several neurological mutants of the mouse. Correlations will be made between the results of these experimental studies and those obtained from observations on human embryos in the Carnegie embryological slide collection.